Increasingly, integrated circuit devices are mounted to their packages face-down, i.e., the surface of the device containing the electronic circuitry faces towards the package. Integrated circuits mounted in this manner are commonly referred to as "flip-chip" devices.
The circuitry of a flip-chip device mounted on a package cannot be probed using conventional electronic probing techniques because the circuitry is physically inaccessible to the probe. Instead, the circuitry of the flip-chip device is typically probed through its backside using an optical probe. An optical probe determines the voltage of a circuit node by sensing infrared radiation through the substrate of the device (i.e., silicon is transparent to near-infrared light). Two types of optical probes are used in the art: (1) reflective optical probes and (2) emission optical probes. A reflective optical probe directs an infrared light beam emitted by a laser onto a surface of the device and measures the polarization of the light reflected from the device. The change in polarization of the light is used to determine the voltage in the circuit. An emission optical probe determines the circuit voltage by measuring the intensity of the infrared light emitted by the circuit.
To optically probe a flip-chip integrated circuit device, optical access must be provided to the backside of the device. At the same time, modern high-speed devices typically require a heat sink or some other heat dissipating mechanism to dissipate the large amounts of heat generated by the device. Unfortunately, placing a heat sink on the device would prevent optical probing.
In view of the foregoing, it would be highly desirable to cool a flip-chip integrated circuit such that it may be optically probed through its backside.